ABSTRACT Septic shock is the leading cause of death in intensive care units and is characterized by severe hypotension linked with a loss of endothelial cell (EC) barrier function. Current research has focused on the inflammatory response in post-capillary venules, but not on resistance arteries despite their critical role in blood pressure regulation. The mechanisms of maintaining barrier function in resistance artery ECs remains unknown and its elucidation is imperative for understanding the hypotension and reduced barrier function in septic shock. Resistance arteries, unlike conduit arteries, have holes in their internal elastic lamina, an extracellular matrix that separates EC and smooth muscle cell (SMC) layers. Within these holes, EC projections form unique signaling microdomains termed myoendothelial junctions (MEJs). Canonically, MEJs allow for EC-SMC communication and have been studied for their involvement in regulating vasodilation. However, this proposal presents a novel function for the MEJ as a structural anchor, based on their ?ball and socket? arrangement. We have previously shown an enrichment of intermediate filaments, structural, and matrix adhesion proteins in the MEJ. Interestingly, my preliminary data highlight shared features of MEJs with filopodia, which also form cell-cell and cell-matrix adhesions. Together, these data suggest that the MEJ may be a key component in the maintenance of EC barrier integrity and therefore a critical regulator in sepsis. The goal of this proposal is to investigate the non-canonical properties of MEJ structures in maintaining EC adhesion to the arterial wall and thus their contribution to barrier function. Aim 1 of this proposal will determine the localization of MEJs within individual ECs to establish their preferential formation at sites more susceptible to barrier dysfunction, i.e. at EC-EC borders, where anchoring to the arterial wall would reinforce the endothelial barrier. I will use en face (whole mount, blood vessel preparations) and scanning electron microscopy to compare MEJ localization distribution in mouse resistance arteries. To determine changes to MEJ formations during sepsis, I will make comparisons of C57Bl/6J mice to a model of barrier dysfunction using LPS treatments, and also to plasminogen activator inhibitor 1 (PAI-1) knockout mice, which have reduced MEJ incidence. Aim 2 of this proposal will investigate the importance of extracellular matrix adhesion proteins, specifically b1 integrin, for MEJ formation and distribution during septic conditions, which have been shown to participate in filopodia-mediated adhesion. I will utilize novel conditional and inducible mice to examine total EC deletion versus arterial EC specific deletion of b1 integrin and measure barrier loss following LPS treatment to assess the role for b1 integrins at the MEJ in barrier dysfunction. Preliminary data demonstrates an increase in b1 integrin localization to the MEJ following an LPS challenge in C57BlJ6 mice. This project will provide novel data that may unveil a unique mechanism by which the ECs of resistance arteries adhere to the arterial wall and will provide potential therapeutic targets for improving the treatment of septic shock.